“I’d found vague descriptions of other copies of the Declaration that turned out to be 19th-century reproductions of the signed parchment in the National Archives, so that was what I was expecting,” Sneff told the Harvard Gazette. “What struck me as significant was that it said manuscript on parchment.”

Sneff was sent a disc with photos of the document.

“When I looked at it closely, I started to see details, like names that weren’t in the right order — John Hancock isn’t listed first, there’s a mark at the top that looks like an erasure, the text has very little punctuation in it — and it’s in a handwriting I hadn’t seen before,” she said. “As those details started adding up, I brought it to Danielle’s attention and we realized this was different from any other copy we had seen.”

The researchers said the signers on the Sussex version are not broken down by state, something that distinguishes it from the copy in the National Archives.

The two dated the document to the 1780s and that it originally belonged to a Duke of Richmond known as the "Radical Duke" for his support of Americans during the Revolutionary War.